Many modern technological applications require precise frequency standards or clocks. For example, very precise navigational systems depend on clocks of extremely high accuracy. Atomic frequency standards form the basis for many such systems. One class of atomic beam standard that has found wide acceptance is based on a cesium beam tube. Cesium beam units are the present basis for most of the national standards of frequency and time. These standards are accurate to a few parts in 10.sup.12.
The cesium beam tube is used to define a very precise microwave frequency. The tube provides a feedback mechanism for controlling the frequency of an oscillator based on the difference between the oscillator frequency and a resonant frequency of the cesium atom. The tube includes a cesium source that operates in a vacuum and various electronically driven components. The components in the tube age with time, and eventually, the entire tube must be replaced.
Each tube is characterized at its time of manufacture. The resulting characterization data is used to specify various operating parameters unique to each tube. The electronic assembly that utilizes the tube requires the operating parameters to operate satisfactorily. In prior art systems, the characterization data is used to compute the values of a number of resistors which form a portion of the electronic assembly. The construction of the typical tube does not provide a convenient location on the tube housing for mounting such electronic components; hence, the selected resistors are mounted on the printed circuit board which connects to the tube. The resistors corresponding to a given tube are shipped with the tube. In these systems, when a tube is replaced, the accompanying resistors must be substituted for those corresponding to the previous tube. This replacement operation typically involves removing the old resistors and soldering the new resistors into a printed circuit card.
This approach has a number of problems. First, the resistors may be lost in transit. Second, the replacement operation may result in damage to the printed circuit board or resistors. Finally, the operation is time consuming and not easily accomplished in the field.
Broadly, it is the object of the present invention to provide an improved atomic beam tube.
It is another object of the present invention to provide an atomic beam tube assembly in which the operating parameters are embodied in components which are permanently connected to the tube.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.